Impedance element



ug- 2y 1944. F. fr. A. WAGNER IMPEDANCE ELEMENT Filed May l, 1941 HG. a.

FIG. 3.

FIG. 2.

A: @www $20202 K D m R W G L MM n. E ha mm En D ML R F Patented Aug. 29, 1944 UNITED STATESz PATENT OFFICE IMPEDANCE ELEMENT Frederick P. A. Warner, Atco, N. J., assigner to The Brown Instrument Company, Philadelphia, Pe., a corporation of Pennsylvanie.

Application Maty I, i941, Serial No. 391,319

10 Claims. ((Sl. 2631-67).

l' core of Bakelite ci similar materiel. The wound resistance wes then coated with varnish or e sinin iler sulistonce to hold it in piece sud'lto protect it troni the deleterious eects 'of moist etnico chere. These prior constructions were for from heine; setisfectory because in c very short time the varnish or like substance cracked open. the wind inse sepcrcted et points which eventuelly resulted in open cirmiits9 shorts, or grounds, the winding become loose enel fell eport, end such resistence constructions retained their originel colihrotiou for cruy o very short time. The above faults, ithos neen round, were caused prinierily hy the widely dliiering amounts of lineair experi@ sion and connection ci the core member enel the Winding teiten es o, unit, end the shrinkuse oi the varnish or such similar substance with which the windings were coated. Varnislies, locquers.,

and like materiels continue to shrink; for e longv period ol time otter they ure initially dried which tact helped to introduce mechonicol stresses sind strains which coused changes in the originel calibration and the eventual failures in such recistences os described above.

rFlic prime object or this invention is to provide a new ond improved molstureproof resistsnee element which ohviotes the shove diiiiculies. Y

In carrying out this invention resistance mow teriel in the form or insulated wire., such as Formex insulated wire, is eccentrically benk wound on a. relatively flexible core which may take the form ci? o. woven gloss nbre tubing. lf desired a. sleeve ci' like material may enclose the wound wire. Due to this arrangement en element is formed `which has a relatively large number of interstices existing throughout the entire structure. These interstices are filled with on impregnating material such asvernlsh, lacquer or the like. The impregnated structure i's then cured bybaking to form a. moisture impervious resistance element. Due to the large number of interstices in the resistance construction the mass by volume of the structure is largely lmpregnating material so that the temperature coetlicient or lli expansion of the resistance construction as o' whole `is controlled by the impregnating material. lDue` to the yielding characteristics ofA the rele tively flexible core and sleeve and the eccentricolu ly bank wound Wire, the resistance construction os a whole may freely expand and contract upon temperature change without loosening or stretching the wire winding or cracking the impregnating materiel. Stresses end strains due to shrinklng of the imcregneting material are herein uvoideol since such shrinkage takes piece uniformly throughout the entire structure both inf j side und out. v

lu eddition to it being on object of this invention to overcome the mechanical and 'electrical icultsos hcreiulieiore'mentioned, it is on object of this invention to provide an improved type ci rnoistureprooi resistance element which will withste-nd unusuclly severe conditions ci vibration without mechenicol ieilure or change in cultureE tion.

It is o further object ci this invention to pro vide cui entirely new type ci resistcnce therniomm eter bulb which will possess the rugged lons last ing qualities enumereted alcove, which cre espe-1 ciellyimportent when the element is to he used.

. under wide and frequent temperoture variations,

und to provide a. resistance thermometer huls which will have little thermal capacity, he interchangeable with older types ci bulbs new in use end he more economical to manufacture.

A further object of this invention is to provide c.

- new und novel .method of melting improved row sistou'ce elements more economically.

The various features of novelty which charrue terize this invention ore pointed out with porticulerity in the claims annexed. to und formino* a port oi this specification. For e. better under stonding" of the invention., however, its solventcges ond specific objects obtained with its use,

reference should he lied to the accompanying drawing end descriptive matter in which is illustrated und described e. preferred embodiment of the invention.

0f the drawing:

Fig. i is en elevation portlr in section illusie troting an element constructed in. accordance with the teachings of this invention;

Fig. 2 is an enlarged view showing c. preferred manner of winding;

Fig. 3 is similar to Fig.' 2 showing e. titiller Windel ng Fig. i ls o. modification of Fig. l illustrating e. lead construction desirable when the resistance element is used as a calibrated resistance element;

Fig. 4AisanendviewofFig.4; and

Fig. 5 is a modincation, in part, of Fig. 1 showing the addition of a second resistance for shifting the characteristic of the resistance element material.

Referring to Fig. i of the drawing the resistance element constructed as illustrated consists of a core member I which may be made from a piece of woven glass nbre tubing. 0n the core I is shown a winding 2 comprising suitably insulated wire, or wires, having such electrical characteristics as it may be desirable for the resistance element to possess. The winding 2 may be covered with a larger piece of woven glass tubing 3 and the ends bound with thread as at 4, to prevent their fraying. The whole assembly is impregnated with a suitable varnish, lacquer, or like substance to stiiIen and provide protection for the resistance element. Insulated lead wires 5, for connecting the element in a circuit, may be anchored directly in the tubing I as at iy and connected, as by soldered joints 1, to extended portions 8 of the resistance wire 2.

As has been mentioned before the actual materials used in the construction of a resistance element in accordance with the principles of this invention are many and the invention may be practiced with varying degrees of satisfactory operation depending upon the materials selected and the manner of associating them. It has been found, however, that for the core member I that woven glass nbre tubing, using a basket type weave, is preferable for many reasons. In the first place glass nbre is quite flexible and hence will yield and not crack. The diagonal direction in which the fibres lie provide greater longitudinal strength to the structure and the looseness of the weave provides larger interstices to take up the impregnating material. The use o! a tubular fabric sleeve possessing a diagonal pattern of weave, as illustrated in the drawings, has the further advantage of 'being able to more readily expand and contract along its longitudinal axis in response to internal forces. Glass nbre has the additional advantage of being able to withstand any tempertures which the now known suitable impregnating materials will withstand, which fact is important in resistance thermometer applications. Glass fibre 'also has a low specific heat while its ability to conduct heat is good.

yFor resistance thermometry rapplications Formex insulated wire has been found preferable because its heat transfer characteristics are better than silk 4and the like. It is also desirable because the volume of the winding is reduced.

The term "eccentrically bank wound" is meant to express a method of winding resistance elements which to the inventor's knowledge has never been used for this purpose before. Formerly when. making resistances by winding wire on a form, the wire was wound in uniform layers one layeron top of the other. It has been found that by starting the winding at one-end of the form and in a sort of random fashion immediately building the winding up to its full thickness and then progressing linearly along the form in a manner to maintain this thickness more or less progressively constant, as the winding progresses, that a winding having more numerous and larger interstices is developed. As with the woven type of core material'the'many and larger interstices ofthistypeofwindingwilitakeuptheimpregnating material more readily and in larger cumferential strain and hence will neither break or be altered in cross section. In Figure 2 an enlarged section view is usedio illustrate this method of winding. The wire` 2 is wound on the core I and the reference numerals on the cross sectioned ends of a group of turns indicate the physical position of each turn -as it might be placedv on the form. Since the winding is of a random character the only proviso vbeing that its average progress is additive linearly at whatever uniform thickness is chosen, the numbers are not meant to set a definite pattern. It is found that with this type of winding an added amount of longitudinal strength results. It may be noted that the free end of the wire when wound as described will always be at the l ance elements so that it is only necessary to remove the excess when calibrating the resistance. With the practice of the winding features of this invention the removal of excess wire in calibrating is simplified and does not alter the fact that the connection of the two wires will always be at the end opposite to that at which the winding was started.

In Fig. 4 and Fig. 4A of the drawing a modified form for connecting the element in a, circuit is illustrated. Leads IA comprising suitable wire or stripsv may pierce the sleeve 3 and core I near the end of the resistance element. cross to the side of the core opposite the point at which they enter, and there may be securely clamped in the core member I by piercing the core member I in two places and bending the leads over as shown. The ends of the resistance wire I may be secured to these leads as by soldering extended portions l to them and when the unit has been impregnated and dried, strong substantial leads are available for its connectibn to a circuit.

Because of their low thermal capacity, their rapid heat transfer characteristics, their ability to withstand severe vibration and their ability to withstand large and rapid temperature changes without change in calibration or mechanical breakdowns, resistance elements constructed in accordance with this invention are especially good for resistance thermometry work.

In constructing a resistance in accordance with the principles of this invention for use as a resistance thermometer the wire 2 as shown in the drawings may be nickel or any other material which has an appreciable temperature coenlcient of resistance.

As illustrated the elements of Figs. 1 and 4 have been shown with the outer sleeve I covering the resistance windings. Omission oi' this outer sleeve 3 will further increase theresponsiveness of the element to changes' in temperature and in such applications wherein theadditional protection afforded by the sleeve is not-needed, it may be omitted without incurring any loss of the other advantages of this invention.

In constructing a resistance in accordance with the principles of this invention for use as a Calibrating resistance for an instrument such as a potentiometer, Wheatstone bridge or the like the wire 2 as shown in the drawing may beof manganin or a like material having a tempera-v ture coeilicient of resistance which is substantially zero.

In Fig. of the drawings part of an element like that illustrated in Fig. 1 is shown with the addition of asecond coil of resistance wire l0. The wire l0 may be manganin wire or the like and be connected in series with the wire 2 by a soldered connection il and in an amount suilicient to shift the characteristic curve of the resistance wire lll to a desired value. The calibration oi' a resistance element constructed in this manner is simplified since excess wire may conveniently and said woven gloss fabric member along their be removed from either the wire 2 or the wire l0 without disturbing the relation of the free ends for connection. If desired the wire i@ need not be connected to the wire 2 ybut may be supplied with separate leads, be composed of any material and serve any desired purpose.

While in accordance with the provisions of the statutes, this invention has beenillustrated and described in the best form now known, it would be apparent to those skilled in the art that vchanges may be made in the form of the appa` ratus disclosed without departing from the spirit of this invention as set forth in the appended claims, and that in some cases certain features of this invention may sometimes be used to advantage without a corresponding use of other features,l

Having now describedthis invention, what I claim as new and desire to secure by Letters' Patent is:

1. An electrical impedance device including in combination, a random wound multi layer electrical impedanceelement which when untreated and unmounted is readily and freely extensible and collapsible along at least one of its axes, a porous member upon which said element is mounted, said porous member when untreated being likewise extensible and collapsible along the same axes along which said electrical iin-v pedance element is extensible and collapsible, and a protective material with which said element and said porous member are impregnated acting` to predominantly control the incremental expanrd sion and contraction ofboth the electrical impedance element and said porous member along their corresponding extensible and collapsible axes to prevent cracking of said protective inaterial o r the development of a condition of strain at any point between said element and the adjacent' portion of said porous member.-

2. An electrical impedance device including in combination, a random wound multi layer electrical impedance element which when untreated and unmounted is readily and freely extensible and collapsible along at least one of its axes, a woven glass fabric member upon which said element is mounted, said woven glass fabric member when untreated being likewise extensible and collapsible along the same axes along which said electrical impedance element is extensible and collapsible, and a protective material with which said element and said woven glass fabric member are impregnated acting to simultaneously control the incremental expansion and contraction of both the electrical impedance element 7s liti corresponding extensible and collapsible axes to prevent cracking of said protective material or the development of a condition of strain at any point between said element and the adjacent portion of said woven glass fabric member.

3. A wound wire electrical device including in combination, an elongated woven fabric core member which when untreated is readily and freely extensible and collapsible along its longitudinal axis, wire random wound on said elongated woven fabric core member around the `longitudinal axis thereof to form a multi layer winding thereon, and a protective material with which said elongated woven fabric core member and said winding are impregnated acting to simultaneously control the incremental expansion and contraction of the elongated woven fabric Y core member and the winding thereon along the longitudinal axis thereof to prevent cracking of said protective material, or the development of a condition of strain at any point between said elongated woven fabric core member and said winding. f

4. A wound wire electrical device including in combination, a tube of woven glass fabric which when untreated is readily and freely extensible and collapsible along its longitudinal axis, wire random wound on said tube of woven fabric around the longitudinal axis thereof to form a multi layer winding thereon, and a protective material with which said tube of woven fabric and said winding are impregnated acting to simultaneously control the incremental expansion and contraction of the tube of woven fabric and the winding thereon along the longitudinal axis thereof to prevent cracking of said protective material, or the development of a condition of strain at any point between said tube of woven fabric and said winding.

5. A wound wire electrical device including in combination, an elongated core member which when untreated is readily and freely extensible and collapsible along its longitudinal axis, wire wound in random fashion on said elongated core member around the longitudinal axis thereof to form a multi layer winding thereon which when untreated is more readily extensible along said axis and a protective material associated with said elongated core member and said winding and acting to' predominantly control the incremental expansion and contraction of the elongated 'core member and the winding thereon along the longitudinal axis to prevent cracking of said protective material, or the development of a condition of strain at any point between said elongated core member and said winding.

6. A wound wire Aelectrical device including in combination, a tube of woven fabric which when untreated is readily and freely extensible and collapsible along its longitudinal axis, wire wound in random fashion on said tube ofwoven fabric around the longitudinal axis thereof to form a multi layer winding thereon which when untreated is more readily extensible along said axis and a protective material associated with said tube oi' woven fabric and said winding and acting to simultaneously control the incremental expansion and contraction of the tube of woven fabric and the winding thereon along the longitudinal axis to prevent cracking of said protective material, or the development of a condition oi' strain at any point between said tube of wovenfabric and said winding. y

"3. A wound wire electrical device including in` combination, a first tube which when untreated is readily and freely extensible and collapsible along its longitudinal axis, wire random wound on said first tube around the longitudinal axis thereof to form a multi layer winding thereon.

said winding, and said second tube of woven fabric.

- wire electrical device which is substantially una second tube covering said winding said second -1 mbe in its untreated condition having extensible and collapsible characteristics similar to those of said first tube, and a protective material with which said f'lrst tube, said winding, and said second tube are impregnated acting to predominantly control the incremental expansion and contraction of the first tube, the winding thereon, and the said second tube 'along the longi-A tudinal axis thereof to prevent cracking of the said protective material. or the' development of a condition of strain at any point between said first tube, said winding, and said second tube.

8. A wound wire electrical device including in combination, a first tube of woven fabric which when untreated is readily and freely extensible and collapsible along-its longitudinal axis, wire random wound on said first tube of woven fabric around the longitudinal axis thereof to form a multi layer winding thereon, a second tube of woven fabric covering said winding, said second tube in its untreated condition having exten sible and collapsible characteristics similar to those of said first tube of woven fabric, and a pro'- teeuve material with which said am tube of woven fabric, said winding, and said second tube are impregnated acting to simultaneously control the incremental expansion and contraction of the first tube of Woven fabric, the windins thereon, and the said second tube of woven fabric along the longitudinal axis thereof to prevent cracking of the said protective material, or the development of a condition of strain at any point between said first tube of woven fabric,

affected by the expansion and contraction of any of its parts comprising thev steps of, supporting a longitudinally extensible and collapsible tube on a mandrel, winding wire on the tube to form the electrical device by starting the winding at one end of the tube and in random fashion immediately building the winding up to its full thickness and then progressing linearly along the length of the tube in a manner to maintain this thickness substantially constant as the winding progresses, and treating the wire wound tube with a relatively large amount of protective material to cause the shrinkage and the thermal coefllcient of expansion and'contraction of the electrical device as a whole to be predominantly controlled by the protective material.

l0. The method of making an electrical impedance element which is substantially unan'ected by the expansion and contraction of any of its parts including the steps of, arranging a conductor of electricity in a random manner upon a first member which when untreated is extensible and collapsiblev along one of its dimensions so that approximately all of said conductor is free to move in unison with incremental movements of said first member uponthe extension or collapse thereof, covering said conductor of electricity with a second member having extensible and collapsible characteristics like those of said `iirst member, and treating the assemblage of said first member, said conductor of electricity, and said second membery with a relatively large amount of protective material which c onrtols the movement of said first member, said conductor, and said second member.

FREDERICK P. A. WAGNER. 

